CYLINDER WAKE CONTROL BY MAGNETIC-FIELDS IN LIQUID-METAL FLOWS

In this paper we are concerned with the control of wake instabilities in the flow of an electrically conducting fluid around a circular cyli nder by means of external magnetic fields. Besides the Reynolds number (Re) a second parameter N appears describing the strength of the magn etic body force. This offers, depending on the direction of the magnet ic field, a large variety of flow configurations and therefore differe nt transition regimes. We perform a numerical simulation of the unstea dy two-dimensional flow and characterize the different flow regimes. S trong magnetic fields are capable to stabilize the 2-D flow and to sup press the shedding of vortices. We present curves of neutral 2-D stabi lity in the (Re, N)-parameter plane separating steady and periodic now regimes. We further perform a linear 3-D stability analysis of the 2- D flow being either steady or periodic and show how the magnetic field influences the 3-D instabilities. We pay special attention to the cas e when the magnetic field is aligned with the oncoming flow. Here we f ind 3-D instability in parameter regions above the 2-D stability curve in the (Re, N)-plane where the flow is 2-D stable (steady). This firs tly confirms a general result of Hunt (J.C.R. Hunt, Proc. Roy. Sec. A 293 (1996) 342) obtained from a stability analysis of parallel flows a nd shows that the magnetic field influences 2-D and 3-D instabilities in a different way. (C) 1998 Elsevier Science Inc. All rights reserved .